1. Field of the Invention
The present invention relates to a magnetron, and particularly relates to a magnetron in which the structure of the choke is altered such that when designing the choke, the design allowance range is expanded so as to realize the optimum efficiency. Thus the unnecessary harmonic waves are more inhibited, and the coupling of the output part is improved due to the impedance of the choke, thereby doubling the output and efficiency.
2. Description of the Related Art
As shown in FIGS. 1 and 2, the conventional magnetron includes: a filament like cathode 1 disposed at the center of the interior; a cylindrical metal anode 2 installed around the cathode 1 to form an interaction space 3; a plurality of vanes 9 installed in a radiative form around the cathode 1, with one end each of the vanes 9 being fixed to the inside of the anode 2; an antenna feeder 11 with one end of it electrically connected to the vanes 9 to transmit electronic energy; permanent magnets 6 and 7 respectively attached to an upper yoke 4 and a lower yoke 5, for forming a closed magnetic circuit to supply magnetic fluxes to the interaction space 3 as shown in FIG. 1; a magnetic pole 8 for forming a magnetic circuit path; an anode seal 18 for serving as a magnetic circuit path and as a body support; and first and second chokes 20 and 21 for inhibiting the harmonic waves coming through the anode seal 18 as shown in FIG. 1.
In FIG. 1, reference code 10 indicates cooling fins, 12 indicates a ventilating tube, 13 indicates an antenna ceramic, 14 indicates an antenna cap, 15 indicates a choke coil for preventing the reverse flow of the harmonic waves toward the power source, 16 indicates a high voltage capacitor, 17 indicates a filter box for removing the unnecessary radiations coming along the supply line, and 19 indicates a filament seal.
The conventional magnetron for microwave ovens constituted as above will be described as to its operations referring to FIGS. 1 to 3.
First, the magnetic fields of the permanent magnets 6 and 7 form a closed magnetic circuit along the upper and lower yokes 4 and 5 and the magnetic poles 8, so that a magnetic field is formed within the interaction space 3 between the cathode 1 and the anode 2.
Then power is supplied to the cathode 1, so that an electric field is formed in the interaction space 3. Then owing to the interaction between the electric field and the magnetic field, the cathode 1 discharges thermionic electrons.
Then the thermionic electrons perform cycloid movements within the interaction space 3, i.e., within the plurality of resonance cavities which are formed by the plurality of the vanes 9. Thus a high frequency energy (hereinafter, referred to as xe2x80x9cmicrowavesxe2x80x9d) which is an electron energy is generated. These microwaves are transmitted to the vanes 9, and then are supplied into the cavity of the microwave oven through the antenna feeder 11.
Under this condition, for example, microwaves of 2450 MHz are generated in the resonance cavities. Besides the fundamental waves, harmonic components having a frequency of integer multiple of that of the fundamental waves are generated simultaneously.
If these harmonic components together with the fundamental waves are supplied into the cavity of the microwave oven, then the shielding of the waves becomes much more difficult because the wavelengths of the harmonic waves are much shorter, with the result that the waves escape to the outside.
Even if the leaked harmonic waves are very weak, they cause serious harm to the human body. Further, they may interfere with the wireless communication. Therefore, in order to inhibit the leakage of the harmonic waves, a filter consisting of a coil and a capacitor is installed at the input side, and at the same time, first and second chokes 20 and 21 which take the form of a metal cylinder are coupled to the interior of the anode seal 18 of the output side.
The structures of the first and second chokes 20 and 21 are as shown in FIG. 3. The first and second chokes 20 and 21 are installed above and below respectively within the anode seal 18. The first choke 20 includes: a cylindrical body 20a for allowing the antenna feeder to pass through; and a flange part 20b extending from the bottom of the cylindrical body 20a toward the anode seal 18.
The second choke 21 includes: a cylindrical body 21a for allowing the antenna feeder to pass through; and a flange part 21b extending from the bottom of the cylindrical body 21a toward the anode seal 18.
The first and second chokes 20 and 21 are designed in the following manner. That is, if it is assumed that the wavelength of the harmonic waves to be removed is xcex, then xcex/4 is adopted as the basic dimension. Then by considering the flanging capacitance, the heights of the chokes are made slightly smaller than xc2xc of the wavelength of the harmonic waves. In this case, however, the external conditions other than the choke height are not matched. As a result, an accurate design becomes difficult, and its application also becomes difficult. Therefore, the capability of inhibiting the harmonic components was limited.
Meanwhile, in order to assemble the first and second chokes 20 and 21 to the output part of the magnetron, there was employed a jig 22 which consists of a multi-stepped guide rod 22a and a base 22b for supporting the guide rod 22a. 
By using this jig 22, the first and second chokes 20 and 21 are assembled in the following manner. That is, the second choke 21 is fitted to the guide rod 22a, and then the first choke 20 is fitted to it, in such a manner that the first and second chokes 20 and 21 should maintain a proper gap between them. In this state, a brazing is carried out to fix them to the anode seal 18.
This will be described in further detail. That is, the second choke 21 is positioned such that its flange part 21b should be disposed below. In this state, the cylindrical body 21a is fitted to the guide rod 22a until the second choke 21 is engaged to a second engaging step 22c of the guide rod 22a, so as to make the second choke 21 secured. Then the flange part 20b of the first choke 20 is positioned so as for it to be disposed below, and then the cylindrical body 20a of the first choke 20 is fitted to the guide rod 22a until it is engaged to a first engaging step 22d. Thus a gap is maintained between the first and second chokes 20 and 21.
Then in order to fix the first and second chokes 20 and 21, brazing stocks are inserted into the anode seal 18. Then they are passed through a high temperature hydrogen brazing furnace. Thus the brazing stocks are melted, and the respective parts are fixed.
Therefore, in the fixing method using the jig 22, the inside diameter of the cylindrical body 20a of the first choke 20 should be necessarily smaller than the inside diameter of the cylindrical body 21a of the second choke 21, if the assembling is to be possible. Thus a limit is imposed on designing the inside diameter which decisively affects the damping of fifth harmonic waves. Consequently, the fifth harmonic wave damping is lowered.
That is, the design should be such that the inside diameter of the first choke 20 should be smaller than that of the second choke 21. Therefore, when designing it by considering the surrounding conditions and the inside diameters of the chokes, the design allowance cannot but be limited.
Particularly, the heights of the chokes should be reduced by considering the flanging capacitance based on experiments, and therefore, an accurate decision of the choke dimensions becomes difficult, with the result that there is a limit in improving the damping of the leakage of the harmonic waves.
The present invention is intended to overcome the above described disadvantages of the conventional art.
Therefore it is an object of the present invention to provide a magnetron in which the structure of the choke is altered, so that when designing the choke, the design allowance range is expanded so as to realize the optimum efficiency, and that the damping of fifth harmonic waves is improved.
In achieving the above object, the magnetron according to the present invention includes: a cathode disposed at the center of the interior; an anode installed around the cathode to form an interaction space; a plurality of vanes installed around the cathode; an antenna feeder with one end of it electrically connected to the vanes to transmit electromagnetic energy from one of cavities; permanent magnets and magnetic poles for forming a closed magnetic circuit to supply magnetic fluxes to the interaction space; an anode seal made of a metal, for serving as a magnetic circuit path and as a body support; and first and second chokes fixed within the anode seal and having each a cylindrical body to make the antenna feeder pass through, for inhibiting the fifth harmonic component coming through the anode seal.
The first choke includes: a first cylindrical body; a first flange part extending from the top of the first cylindrical body toward the anode seal; and a supporting means extending from the first flange part in parallel to the first cylindrical body.
The second choke includes: a second cylindrical body; and a second flange part extending from the top of the second cylindrical body toward the anode seal. Thus the first and second chokes maintain a proper gap between them due to the supporting means.
The first choke includes: a first cylindrical body with its opening directed toward the anode, and having a height of 2.0-2.6 mm; and a first flange part extending from the top of the first cylindrical body toward the anode seal, the first choke being fixed on an inner upper portion of the anode seal. The second choke includes: a second cylindrical body having a height of 3.2-3.8 mm, and with its opening being directed in a direction same as that of the first cylindrical body; and a second flange part extending from the top of the second cylindrical body toward the anode seal. Thus the second choke maintains a gap of 1.4-1.8 mm from the lower end of the first cylindrical body.